Double reflector antenna with polarization rotating main reflector

ABSTRACT

A double reflector antenna system has a polarization rotating main reflector which is symmetrical, a polarization dependent subreflector which is symmetrical, and a feeder arranged with its aperture between the main reflector and the subreflector to deliver energy to or receive energy from the subreflector, the aperture being in a plane perpendicular to the symmetry axis of the two reflectors and having an oval shape facing the subreflector.

ite States Patent 1191 Carlsson et al.

DOUBLE REFLECTOR ANTENNA WITH POLARIZATION ROTATING MAIN REFLECTOR Inventors: Eric Ake Ragnar Carlsson,

Goteborg; Olof Gustav Robert Dahlsjo', Molndal; Go'ran Roland Karlsson, Nygard; Kent Morgan Pettersson, Goteborg, all of Sweden Assignee: Telefonaktiebolaget LM Ericsson,

Stockholm, Sweden Filed: Apr. 4, 1973 Appl. No.: 347,843

Foreign Application Priority Data Apr. 24, 1972 Sweden 5357/72 I US. Cl 343/756, 343/781, 343/786, 343/837 Int. Cl. IlOlq 19/00 Field of Search 343/756, 781, 837, 786

[111 3,82,11 [4 June 25, 1974 References Cited UNITED STATES PATENTS 2,961,659 11/1960 Kuecken 343/786 3,195,137 7/1965 Jakes 343/756 Primary ExaminerEli Lieberman Attorney, Agent, or Firm-Hane, Baxley & Spiecens ABSTRACT A double reflector antenna system has a polarization rotating main reflector which is symmetrical, a polarization dependent subreflector which is symmetrical,

and a feeder arranged with its aperture between the main reflector and the subreflector to deliver energy v to or receive energy from the subreflector, the aperture being in a plane perpendicular to the symmetry axis of the two reflectors and having an oval shape facing the subreflector,

8 Claims, 4 Drawing Figures DOUBLE REFLECTOR ANTENNA WITH POLARIZATION ROTATING MAIN REFLECTOR The present invention relates to a double reflector antenna system with a polarization rotating main reflector, a polarization dependent subreflector and a feeder arranged to supply energy to or receive energy from the subreflector.

Owing to the fact that in certain double reflector antennas the polarization of the radiant energy delivered from the feeder within certain parts of the subreflector of the antenna does not correspond to the direction of polarization, at which this reflector is intended to reflect completely the incoming radiant energy, unwanted side lobes arise.

Usually the aperture of the feeder in known antennas of the kind in question has been rectangular, so that the such polarization problem has been present.

Previously feeders with round aperture in antennas have been used for special purposes, for example in antennas with lobe rotation, where a circular feeder is turned in a characteristic way with the maintained polarization direction of the antenna.

An object of the present invention is to obtain an antenna where the occurrence of the abovementioned kind of side lobes is at least to a great extent, prevented.

The characteristics for an antenna system constructed according to the invention are defined in the appended claims.

The'invention will be described more in detail with reference to the accompanying drawing, where FIG. 1 schematically shows an example of an antenna of the kind to which the invention refers,

FIG. 2 shows a front view of the feeder of the antenna,

FIG. 3 shows, in a radiation diagram, the difference between measured side lobes for an earlier known antenna and an antenna system according to the invention and FIG. 4 shows schematically a front view of the subreflector of the antenna system.

In FIG. 1, 11 indicates a polarization rotating main reflector, 12 a polarization dependent subreflector and a feeder. The feeder 10 is arranged to supply energy to or receive energy from the subreflector 12. The arrowed-ray in FIG. 1, indicates how the radiant energy from the feeder 10 is reflected by the subreflector 12 towards the main reflector 11 and then is transmitted through the subreflector 12 owing to occurred polarization rotating in the main reflector 11.

As already mentioned it has been shown in practice that known antennas of this kind have been impaired by unwanted side lobes caused by the above-mentioned polarization faults. In FIG. 3 the curve G shows a radiation diagram for an earlier known antenna in a diagonal plane through a subreflector constructed with vertical wires for the reflection of vertical polarized signals. In the diagram the letter S indicates the radiation density in decibels and 9 the angle from the symmetry axis of the antenna. As is evident from the diagram the curve G shows a considerable maximum outside the side lobes close to the main lobe.

To eliminate the mentioned maximum in the radiation diagram such modification has been made according to the invention so that the feeder 10 has been formed with an aperture with an oval shape facing the subreflector 12, the direction of the feeder relative to the subreflector, that is turning around an axis in the plane of the paper in FIG. 2, and the oval form of the aperture have been chosen so that deviations in the polarization dependent transmissionand reflection qualities of the subreflector in certain regions compared with the corresponding qualities of the subreflector in its central part are as much as possible compensated. The exact direction and embodiment of the aperture of the feeder are dependent on the dimensions and embodiment of the subreflector. By suitable choice of the eccentricity degree of the aperture of the feeder also a wanted distribution of the radiant energy over the surface of the subreflector is obtained within certain limits.

In FIG. 3 the curve N indicates the corresponding radiation diagram for an antenna system formed according to the invention. As is evident from a comparison between the curves the antenna according to the inven tion gives a considerably better relation between main lobe and side lobes.

In certain cases it has been found suitable to form the aperture elliptic and to aim the feeder so that the major axis of the aperture will be perpendicular to the polarization direction of the energy reflected from the subreflector, that is, if the subreflector is made of a grip reflector known per se with the grid wires lying in between parallel, vertical planes, the major axis will lie in a horizontal plane.

The feeder shown in FIG. 2 is formed with a wall 21 dividing the aperture, which wallextends along the major axis of the oval. Thus in a simple and per se known way driving the feeder is made possible in a socalled difference mode in a plane perpendicular to the wall without the qualities of the arrangement being noticeably deteriorated when driving the feeder in a socalled sum mode, in which form of driving the advantages of the invention are most outstanding and desirable.

The subreflector 12 shown in FIG. 4 is in well-known manner formed as a plastic shell, in which vertical metal wires 41 are embedded. These metal wires reflect waves arriving at the subreflector, if these have vertical polarization, while on the other hand waves with horizontal polarization pass through. According to the invention the feeder 10 has an oval aperture facing the subreflector 12 with the largest diameter of the aperture perpendicular to the direction of the metal wires We claim:

1. A double reflector antenna system comprising a polarization rotating main reflector, a polarization dependent subreflector disposed opposite said main reflector, and a feeder means disposed adjacent said main reflector in such a way that signal energy from said feeder means is transmitted to said subreflector and reflected therefrom to said main reflector or external signal energy received by said main reflector is reflected therefrom and via a further reflection from said subreflector to said feeder means, said feeder means including a tubular aperture aimed at said subreflector and having a cross-section which is elliptical with a major axis orthogonal to the polarization direction of the energy reflected from said subreflector.

2. Arrangement of a double reflector antenna comprising a polarization rotating main reflector which is symmetrical about a given axis, a polarization dependent subrefiector facing said main reflector and being symmetrical about said given axis, and a feeder means having an aperture between said reflectors and disposed to deliver energy to or receive energy from said subrefiector, said aperture being in a plane orthogonal to said given axis and having an oval cross-section in said plane.

3. Arrangement according to claim 2, characterized in that the aperture has an elliptic form with the major axis perpendicular to the polarization direction of the energy reflected from the subrefiector (l2).

4. Arrangement according to claim 2, characterized in that the feeder is supplied with at least one wall (12) dividing the aperture (20).

5. Arrangement according to claim 4, characterized in that the wall (21) extends along the largest diameter of the aperture.

6. Arrangement according to claim 2, characterized in that the subrefiector (12) consists of a grid reflector known per se, the feeder being so directed that the largest diameter of the aperture (20) is perpendicular to the direction of the grid wires of the subreflector (l2).

diameter in the aperture. 

1. A double reflector antenna system comprising a polarization rotating main reflector, a polarization dependent subreflector disposed opposite said main reflector, and a feeder means disposed adjacent said main reflector in such a way that signal energy from said feeder means is transmitted to said subreflector and reflected therefrom to said main reflector or external signal energy received by said main reflector is reflected therefrom and via a further reflection from said subreflector to said feeder means, said feeder means including a tubular aperture aimed at said subreflector and having a cross-section which is elliptical with a major axis orthogonal to the polarization direction of the energy reflected from said subreflector.
 2. Arrangement of a double reflector antenna comprising a polarization rotating main reflector which is symmetrical about a given axis, a polarization dependent subreflector facing said main reflector and being symmetrical about said given axis, and a feeder means having an aperture between said reflectors and disposed to deliver energy to or receive energy from said subreflector, said aperture being in a plane orthogonal to said given axis and having an oval cross-section in said plane.
 3. Arrangement according to claim 2, characterized in that the apertuRe (20) has an elliptic form with the major axis perpendicular to the polarization direction of the energy reflected from the subreflector (12).
 4. Arrangement according to claim 2, characterized in that the feeder is supplied with at least one wall (12) dividing the aperture (20).
 5. Arrangement according to claim 4, characterized in that the wall (21) extends along the largest diameter of the aperture.
 6. Arrangement according to claim 2, characterized in that the subreflector (12) consists of a grid reflector known per se, the feeder being so directed that the largest diameter of the aperture (20) is perpendicular to the direction of the grid wires of the subreflector (12).
 7. Arrangement of a double reflector antenna with a polarization rotating reflector, a polarization dependent subreflector and a feeder arranged to deliver energy to or receive energy from said subreflector characterized in that said feeder has an aperture with an oval shape facing said subreflector with a wall extending along the largest diameter of the aperture for dividing the same into different regions.
 8. The arrangement of claim 7 wherein said subreflector comprises a plurality of parallel grid wires which are disposed orthogonally with respect to the largest diameter in the aperture. 